This study aims to examine the correlations of plasma and red cell alprazolam levels with symptoms, mood, and psychomotor performance in panic patients upon initiation of treatment and abrupt withdrawal of chronic treatment. After a 1 mg dose, the patient will be monitored for 24 hours with periodic observation, mood scales, performance tasks, and blood samples for drug levels. After 8 weeks of treatment with alprazolam 4 mg daily, the patient will be monitored similarly for two 24-hour periods separated by one week of treatment.